Communication systems, radar systems, signal processors, control and timing systems require oscillators in order to carry out their intended functions; advanced signal generation systems require oscillators having low phase and FM noise and good temperature stability. In order to obtain low phase and FM noise, the oscillator should have a high loaded Q, since the phase and FM noise of an oscillator are determined by its Q. Oscillator temperature stability, on the other hand, depends principally upon the thermal expansion coefficient of the resonator so that the lower the thermal expansion coefficient, the better the temperature stability.
Prior art oscillator configurations for achieving a high Q have included large size cavities (such as circular cylindrical cavities, rectangular cavities, coaxial cavities and low frequency helical cavities). In order to obtain good temperature stability, materials utilized in these cavities commonly include metallized fuzed quartz, which unfortunately suffers from its high cost, weight and size. As additional schemes for stabilizing the operation of an oscillator, components such as surface acoustic wave (SAW) and bulk acoustic wave (BAW) delay lines have been used. However, these types of delay lines suffer the following disadvantages; presetting of the oscillation frequency cannot be achieved with precision without extreme difficulty; high insertion loss; high dispersion which limits wideband operation; deficient temperature stability; problems with hysteresis, potential aging and multimode operation; fabrication, particularly of high frequency delay line transducers, is difficult; the operation frequency and temperature ranges are limited; phase shift components are required; and hermetic sealing is required to avoid loading perturbation.